Permanent magnet type rotary electric machines have been improved in terms of performance rapidly with the development of high residual magnetic flux density magnets. For this reason, the permanent magnet type rotary electric machines have been used in all phases. Particularly, high energy efficiency has been requested for electric motors for industrial use or for household use in view of recent environmental regulations. Thus, the application ratio of the permanent magnet type electric motors tends to be extremely high.
In addition, since a highly efficient system configuration can be attained as an auxiliary motive power source for an engine or a transmission in an electric motor for a vehicle, the application ratio of a permanent magnet synchronous electric motor is high and it is positioned as an essential component.
On the other hand, in construction machines vehicles, due to a severe request for transformation into an eco-friendly type, reduction in fuel consumption based on motorization is an absolute must. Here, an electric motor for a construction machine vehicle, particularly for a hydraulic excavator has to serve as a generator motor for supplying auxiliary motive power to an engine and a hydraulic pump and supplying electric power to all electric components disposed inside the vehicle. In addition, due to the configuration in which the electric motor is placed in a small space between the engine and the hydraulic pump, the electric motor inevitably has to be designed to achieve reduction in size and increase in output density (to be designed to achieve increase in output power per unit volume). Further, since the electric motor is operated with a high output under a high temperature environment due to heat transfer from the engine and the hydraulic pump, it is necessary to pay special care to a cooling configuration in the electric motor.
According to a concept of a generator motor in which special care is paid to a cooling configuration for a construction machine vehicle represented by a hydraulic excavator, a permanent magnet type synchronous motor can be formed to have a configuration with high efficiency and with a small amount of heat generation. It is, however, essential to use another cooling means so that the generator motor can be driven under an environment where the generator motor placed in the small space between the engine and the hydraulic pump is apt to be affected by heat transfer from the engine and the hydraulic pump.
To this end, a means for forcibly cooling down the generator motor, particularly for directly cooling down the generator motor with oil is the most suitable. A background-art structure in which oil directly cools down the generator motor has been proposed, for example, in Patent Literature 1. According to the Patent Literature 1, cooling oil forcibly circulated is injected to center portions of slots through an oil passage provided in a bracket holding the motor, that is, among motor windings. With this configuration, the windings can be cooled down along an axial direction of the motor.